Total Synthesis of (−)-Spirotryprostatin B

Rapid assembly of the backbone of spirotryprostatin B (4) was achieved by employing a MgI2-catalyzed ring-expansion reaction of spiro[cyclopropane-1,3′-oxindole] 1 and alkynyl imine 2 to yield advanced intermediate 3. Introduction of the prenyl side chain was accomplished by aldehyde olefination through a Julia–Kociensky reaction, a transformation that greatly facilitates late-stage derivatization for biological studies. TIPS=triisopropylsilyl.